Sweep, Loading… Unloading II

In the first article of this series we studied how the setting of a V-loop doesn’t put any load in the rod. The momentum of the line travelling backward is transferred to the water, without affecting the rod tip. In many spey casting technical works we find another purported source for that mythical rod pre-loading: the rod motion from the tilted sideways position at the end of the sweep into the more vertical position suitable for starting the forward cast, a maneouver also known as circling-up. A quote from the internet about this circling up and its consequences puts things in perspective:

It is intended to transfer the rodloading created during the Sweep, on through to the Forward Cast, in a continuous, uninterrupted fashion… no stopping of the rod, no load-unload-load action… thereby maintaining continuous loading of the rod.

As H.G. Wells wrote: It sounds plausible enough tonight, but wait until tomorrow.

Will tomorrow be able of invalidating plain logic?

As we have seen in the first part of this study rod bend comes from a force. After the sweep is finished the line moves on its own backward; the rod pulls on the line making it turn and a loop is formed.

– Well, for that to happen the rod has to exert a force on the line, and the line exerts the same force -action/reaction- on the rod in the opposite direction, right?

– Yes, of course.

– So the rod gets loaded, right?

– No, slo-mo says it doesn’t and so does physics.

Let’s take a look to the equation for force:

F = m.a

What this equation states is that force is directly proportional to mass (weight in layman’s terms) and acceleration (change in velocity). The bigger the mass the bigger the force needed to accelerate it; the bigger the acceleration the bigger the force applied. So for a force to be increased we could increase m, a or both.

So what happens to the mass of the line and its acceleration -and consequently to force and then rod load- in those two phases of spey casting known as sweep and circling-up?

During the sweep we are applying force to the whole length of line at play in order to form a loop; during circling-up we exert force only on the short piece of line which is actually turning around in the loop front, the part of the line changing direction but not on the rest of it. During the sweep we are pulling on a much bigger mass.

What about acceleration? During the sweep we have to accelerate the line significantly to form a loop; when circling-up the rod is not accelerating anymore, for the caster moves it to the key position leisurely, without the intention of applying any significant force. During circling-up we are pulling with much less acceleration.

The logical conclusion? The force bending the rod on the sweep is comparatively big and decreases hugely when the sweep ends. In fact the force exerted on the rod by the line during circling-up is so low that the amount of bend left is irrelevant. Some video to clarify things:

The following pictures correspond to three frames taken from the video above: they show both the difference in the mass the rod is pulling on, and the difference in rod bend between the sweep and the circling up.

The sweep applies significant force to the whole line. The rod is bent.

End of the sweep. No force applied to the rod or the line. Note how the line has lost tension and the rod is straight.

An instant during circling-up. The rod is pulling only on that piece of line inside the red circumference, so there is no appreciable bend in it.

More video:

Is it that important to be aware of these intricacies? It is, in my opinion, if only for one reason: if you train or fish focusing on getting some impossible pre-load, you won’t be paying attention to the things actually defining spey casting efficency, namely: minimum anchor, maximum live line in the V-loop, all that aligned with the target and as close to the forward rod tip trajectory as possible.